Drive linkages are employed in automotive vehicles between the prime mover, typically an internal combustion engine, and the driven wheels. Such drive linkages generally include a line of rotating components from the rotating output of the engine to the rotating input of the driven wheels. A transmission is typically employed in order to vary the ratio of speeds between the engine output and the driven wheel input. The transmission is shifted to give the operating speeds or power ratios required. A clutch, torque converter or fluid coupling is also employed for interrupting power transmission between the engine output and the driven wheels.
A manual transmission typically includes two shafts, one forming the input shaft to which power is applied and the other forming the output shaft that is ultimately connected, usually through a differential mechanism, to the driven wheels. In its most common form, at least two pair of mated gears are mounted respectively on the input and output shafts, and the respective pairs of gears are continuously engaged with one another. One gear of each pair is keyed non-rotatably to its respective shaft while the other is freely rotatable on its respective shaft. Thus, although the gears are continually meshed, with nothing more, rotation of the input power shaft does nothing to cause rotation of the output shaft.
In order to selectively key the rotatably mounted gear to its respective shaft, a gear clutch or synchronizer is located adjacent the rotatably mounted gear. A synchronizer mechanism is one common form of gear clutch. Synchronizer mechanisms are small clutches maintained engaged by the change-speed control during the time required to obtain the equalization of the angular speeds of the elements to be clutched, e.g., the adjacent gears. In these synchronizer mechanisms, a synchronizer sleeve is disposed about a hub fixed to a shaft. The sleeve is moveable axially relative to the hub on the shaft and into or out of engagement with the adjacent gear. The sleeve includes an indexing mechanism having retaining mechanisms. The synchronizer mechanism also includes an intermediate clutch ring between an adjacent gear and the sleeve. The intermediate clutch ring includes an interior cone shaped surface that interacts during gear selection with an exterior cone shaped surface on the adjacent gear through friction. The intermediate clutch ring also includes external gear teeth that are engaged by internal splines on the sleeve. During gear selection, a shift lever moves the sleeve axially along the shaft in the direction of the intermediate clutch ring and an adjacent gear. As the sleeve moves, the external gear teeth of the intermediate clutch ring and the internal splines of the sleeve contact one another and cause the intermediate clutch ring and the sleeve to rotate with the same angular velocity. However, the internal splines of the sleeve are prevented from fully engaging with the external gear teeth of the intermediate clutch ring until the angular velocities of the adjacent gear and the intermediate clutch ring are the same. Simultaneously, the retaining mechanism of the sleeve forces a strut of the retaining mechanism to move laterally and contact the intermediate clutch ring. As the strut contacts the intermediate clutch ring, the interior cone shaped surface of the intermediate clutch ring is forced against the exterior cone shaped surface of the adjacent gear. The contact between the interior cone shaped surface of the intermediate clutch ring and the exterior cone shaped surface of the adjacent gear creates friction and causes the adjacent gear and intermediate clutch ring to rotate at the same angular velocity.
Once the angular velocities of the adjacent gear and the intermediate clutch ring are approximately the same, the internal splines of the sleeve fully engage with the external gear teeth of the intermediate clutch ring as the sleeve is moved further in the direction of the intermediate clutch ring and the adjacent gear. The further movement of the sleeve in the direction of the adjacent gear causes the retaining mechanism to be overcome. Once the retaining mechanism is overcome, the retaining mechanism no longer forces the strut against the intermediate clutch ring. As a result, the interior cone shaped surface of the intermediate clutch ring is no longer forced against the exterior cone shaped surface of the adjacent gear and friction between the interior cone shaped surface of the intermediate clutch ring and the exterior cone shaped surface of the adjacent gear is removed. The sleeve subsequently becomes fully engaged with the adjacent gear. However, there is a lapse of time between when the sleeve is fully engaged with the intermediate clutch ring and when the sleeve becomes engaged with the adjacent gear. The removal of friction between the interior cone shaped surface of the intermediate clutch ring and the exterior cone shaped surface of the adjacent gear coupled with drag present within the transmission may cause the adjacent gear to change in angular velocity relative to the intermediate clutch ring and the sleeve. This problem is particularly pronounced in colder weather and before the transmission has had the opportunity to warm to operating temperature. When this happens, the adjacent gear and the sleeve are forced together while having different angular velocities. Forcing the adjacent gear and sleeve together increases wear on transmission parts, thereby decreasing service life. In addition, forcing the adjacent gear and sleeve together while they are rotating with different angular velocities may result in difficult, loud and notchy shifting, which is undesirable.
It is, therefore, desirable to provide a synchronizer mechanism for a manual transmission that overcomes the problems when friction is lost between the interior cone shaped surface of the intermediate clutch ring and the exterior cone shaped surface of the adjacent gear as the synchronizer sleeve fully engages with the intermediate clutch ring.